We propose that the cytochrome P-450 mixed function oxidase reaction contains two reactions, one an NADPH oxidase and the other a monooxygenase reaction. To date attempts to study stoichiometries of the monooxygenase reaction have been confused by the generation of H2O2, a component of the NADPH-oxidase. We have developed a mechanism which envelopes both reactions and will attempt to show that during the mixed function oxidase reaction, uncoupling of active oxygen with subsequent discharge of oxygenated cytochrome P-450, yields H2O2. Influence of different substrates on the stoichiometries will be examined.